QUESTION

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Impedance effects from inductor/capacitor on antenna band select pin

Hi, I am working on tuning a SR4C033-R but I cannot find any resources on how the inductor or capacitor on the band select pin affects the antenna impedance, which is helpful to know for tuning using a Smith Chart.

A similar question here was asked but the answer did not state exactly how this pin affects the impedance.

Are there any resources available that explain this?

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1 Answer

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Hi Lance,

The inductor will add length to the L3 pin making the antenna look longer therefor lowering the frequency. So the 6.8nH inductor adds more length than the 3.3nH inductor.  If you put a zero ohm resistor on the L3 pin you should see the natural resonance of the antenna element itself and it should be operating above the 900MHz band. These values are only applicable to our evaluation boards in free space and will need to be adjusted for your device's ground plane length and housing.

Best regards,

Geoff S.

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